Microwave drying system



Feb. 11, 1969 v RYMAN ET AL 3,426,439

MICROWAVE DRYING SYSTEM Filed Feb.'l6, 1967 Sheet of 5 FIG. I

IMPEDANCE W men VE DUMMY an M 0R wfi'gg I4 54 v A ,55 m SUPPLY 1 r socooLm SOURCE mm W RYMA sun R scamm- ATTORNEYS Feb. 11, 1969 RYMAN ET ALMICROWAVE DRYING SYSTEM Sheet 2 I pf 5 Filed Feb. 16, 1967 F l G 3INVENTORS IVAN RYMAN GUNTER SCHMIDT BY tgd wlw 4 ATTORNEYS I Filed Feb.16, 1967 I Sheet 3 of C FIG. 4(0) Feb. 11, 1969 l.- RYMAN 6,

MICROWAVE DRYING SYSTEM r 68 as I FIG. 4 (b) FIG. 5

' INVENTORS ilVAN RYMAN GUNTER SCHMIDT ATTORNEYS Feb. 11, 1969 l. RYMANT MICROWAVE DRYING SYSTEM sheet 4 of Filed Feb. 16, 1967 F l G. 7

INVENTORS IVAN RYMAN BY GUNTER SCHMIDT CONT L MEANS- MICROWAVE F l G.

ATTORNEYS Feb. 11,1969 [.RYMAN ET AL 3,426,439

MICROWAVE DRYING SYSTEM Filed Feb. 16,1967 Sheet 5 of 5 H H [1 H A4 i ii i 1 1 II I: -H H i H I L Ms, L

F I s. l

mvmons F G. IVAN RYMAN GUNTER SCHMIDT BY h4g1 4 W ATTORNEYS UnitedStates Patent Office 3,426,439 Patented Feb. 11, 1969 ABSTRACT OF THEDISCLOSURE An apparatus useful for drying film and the like at highspeeds by the application of microwave energy. A conductor isserpentined through a perforated surface which may, for example, besubstantially cylindrical or planar. Microwave energy is coupled to theconductor to establish a fringing electromagnetic field through whichthe film is pulled. The film is spaced from the surface by an airbearing formed by exhausting air through the surface perforations.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates generally to apparatus useful for drying material and moreparticularly to apparatus employing microwave electromagnetic fieldsadapted to very rapidly dry a continuously moving film strip.

As the quantity of wet processed film used by both the military andindustry has continued to mount, the need for improved film dryingapparatus has become increasingly apparent. Conventional prior art filmdrying techniques, typified by hot air impingement, have been pushedalmost to their limit in both efiiciency and speed and yet are not ableto satisfactorily cope with the increasingly demanding applicationrequirements.

DESCRIPTION OF THE PRIOR ART The prior art reveals that varioustechnologies have been applied to the problem of film drying in anattempt to increase both speed and efiiciency without sacrificingquality. Probably the most prevalent prior art technique involvesbringing high velocity hot air into contact with the film. Otherattempts have involved the application of ultrasonic, infrared, laser,and microwave technologies to the drying problem. Thus far however, noneof these various attempts has provided a satisfactory drying apparatuscapable of efficiently operating on various widths of film at speeds inexcess of about 100 ft./min.

The prior art attempts at drying by utilizing microwave energy haveusually involved an apparatus comprised of a slotted serpentinedwaveguide having a rectangular cross-section compatible with thefrequency employed. In such an apparatus, the film is pulled through theslots and is thus exposed to the microwave energy being propagatedthrough the guide. Such an arrangement presents many problems inaddition to that of tailoring the absorption of power to suit the filmemulsion characteristics.

For example, it has proved exceedingly diflicult to precisely pass thefilm through the waveguide slots at a high speed without damaging thefilm by physical contact. It has also proved difficult to prevent thenonuniform dissipation of energy in the film which causes nonuniformdrying. Additionally, drying in this manner has resulted in condensationwithin the waveguide thus modifying the characteristics thereof.

SUMMARY OF THE INVENTION The present invention is directed to animproved apparatus for effectively drying material at higher speeds thanhas heretofore been economically possible.

Briefly, the present invention is directed to an apparatus utilizing agas bearing to enable a strip of material to be efficiently exposed toor illuminated by a microwave electromagnetic field.

The term microwave as used herein will refer primarily to the portion ofthe electromagnetic spectrum from 900 to 30,000 megacycles (even thoughany radio wave above 1000 kilocycles is, strictly speaking, amicrowave). In this microwave range, four frequencies have beenpreassigned by the Federal Communications Commission for industrial,scientific, and medical purposes (the so-called ISM frequencies). Theseare, respectively, 915, 2450, 5800, and 22,125 megacycles. Of these, thetwo lower frequencies are those most commonly used in industry and aresometimes referred to as the L and S bands. It will be assumed that themicrowave energy utilized by the embodiments disclosed herein will fallin one of these two bands.

In accordance with one aspect of the preferred embodiment of theinvention, an air bearing is formed by exhausting air through aperforated surface which can, for example, be substantially cylindricalor planar. The material strip, which can comprise wet processed film,for example, is pulled over the surface but is spaced therefrom by theair bearing. Thus, there is no physical contact between the material andthe surface and accordingly, the likelihood of film damage is reducedconsiderably as compared to prior art arrangements.

In accordance with a further aspect of the preferred embodiment of theinvention, the microwave field through which the material is pulled, isdeveloped by coupling a microwave generator to a conductor orilluminator disposed in the perforated surface. The illuminatorpreferably comprises a slow wave structure or transmission line which,in response to the application of microwave energy thereto, develops apronounced standing wave pattern or fringing field along its length.Energy can be coupled to the illuminator from a standard transmissionline through an impedance matching coupler.

In accordance with one feature of the invention, the illuminator,comprises an electrical conductor serpentined across the path ofmaterial movement. In accordance with another feature of the invention,the illuminator conductor is hollow to permit a coolant to flowtherethrough.

In accordance with another feature of the invention, the microwaveenergy is applied to the illuminator in such a manner that the wetterportions of the material are exposed to a relatively weakerelectromagnetic field than are the drier material portions.

In accordance with one alternate embodiment of the invention, theserpentined illuminator is formed to define two spaced rows ofilluminator sections, thus enabling the material to be pulled along apath between the rows of sections.

In accordance with a further departure from the preferred embodiment ofthe invention, the illuminator sec tions are disposed at an angle withrespect to the material path in order to prevent nonuniform drying dueto aligned node points.

In accordance with a further feature of an alternate form of theinvention, means are provided for enabling It is pointed out thatseveral attractive operating characteristics result as a consequence ofconstructing an apparatus in accordance with the preferred embodiment ofthe invention; notably, condensation adjacent the apparatus issubstantially eliminated inasmuch as the exiting air carries the watervapor away. Additionally, the natural tendency of the material to curlas it dries is reduced by conforming it to a cylindrical surface.

DESCRIPTION OF THE DRAWINGS FIGURE 1 schematically illustrates a dryingsystem employing a plurality of drying units in accordance with thepresent invention;

FIGURE 2 is a schematic block diagram illustrating a drying unit inaccordance with the present invention together with means for supplyingair and microwave energy thereto;

FIGURE 3 is a perspective view of a preferred structural embodiment ofthe invention;

FIGURE 4a is a side view of a preferred structural embodiment of theinvention;

FIGURE 41) is an enlarged fragmentary sectional view illustrating meansfor varying the length of an illuminator section;

FIGURE 5 is a sectional view taken substantially along the plane 55 ofFIGURE 4;

FIGURE 6 is a schematic sectional view illustrating the electromagneticfield formed by the illuminator sections and the manner in which thefield intersects the material to be dried;

FIGURE 7 schematically illustrates an alternate embodiment of theinvention;

FIGURE 8 schematically illustrates a still further embod iment of theinvention;

FIGURE 9 illustrates a side view of the preferred embodiment of theinvention showing how it can be utilized to handle material of differentwidths;

FIGURE 10 is a schematic illustration of a further alternate embodimentof the invention;

FIGURE 11 is a schematic diagram of a still further alternate embodimentof the invention; and

FIGURE 12 is a schematic diagram of a still further alternate embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now called toFIGURE 1 which illustrates a system 10 comprised of a plurality ofdrying units 12 suitable for drying material such as strip material 14.Although the strip material 14 can comprise many different materials,the exemplary material which will be most often referred to herein willbe wet processed film. However, it should be appreciated that the system10 can be utilized to dry other materials, e.g. the coatings on paper,fabric, or any synthetic or natural fiber. Further, although, as will bebetter appreciated hereinafter, the invention finds its greatest utilityin drying continuous strips of material, it is also useful for dryingsheet material.

As shown in FIGURE 1, the material 14 can be fed from some supply means,such as roll 16, around a series of drying units 12 to take-up roll 18.A pair of idler rollers 20 and 22 are illustrated for guiding thematerial 14.

Although six drying units 12 are illustrated in the system 10 of FIGURE1, it is pointed out that the number of drying units required depends,of course, upon the particular application. Thus, one drying unit 12 maybe adequate to rapidly dry some materials while a greater number ofdrying units 12 arranged in tandem as shown in FIGURE 1 may be requiredfor other materials. Inasmuch as the drying units 12 of FIGURE 1 are allintended to be substantially identical, except for perhaps the amount ofpower supplied to each, the remaining por tion of the specification willbe primarily directed to a description of the structure and operation ofonly a single drying unit 12.

Attention is now called to FIGURE 2 which illustrates a schematic blockdiagram of a single drying unit 12 in accordance with the presentinvention, together with apparatus coupled thereto necessary for itsoperation. Briefly, in accordance with the present invention, the dryingunit 12 is comprised of a drum 30, having a cylindrical surface aroundwhich the strip material or film 14 passes. As will be explained ingreater detail hereinafter, the drum surface has a plurality ofperforations therein through which a gas such as air is exhausted toform an air bearing to space the film 14 from the surface. Moreparticularly, an air supply source 34 is provided which is coupled byhose 35 to a plenum chamber 36 defined within the drum 30. By supplyingair through the hose 35, to the plenum chamber 36, the air will beexhausted through the perforations defined in the drum surface to forman air bearing to consequently space the film 14 from the surface. Inthis manner, the film 14 can be pulled over the drum surface out ofphysical contact therewith.

In accordance with a further aspect of the present invention, amicrowave electromagnetic field is generated which intersects the pathof the film 14 as it is pulled around the drum 30. As will be betterexplained hereinafter, a serpentined conductor or illuminator 40 isprovided within the drum 30, preferably coincident with the drumsurface, to develop a fringing electromagnetic field. That is, amicrowave generator 42, e.g. of the magnetron type, is utilized tosupply microwave energy through an impedance matching coupler 44 to oneend of the illuminator 40. A dummy load 46 is coupled to the second endof the illuminator 40 in order to absorb any energy not attenuated inthe drying unit 12.

As will be seen hereinafter, the illuminator 40 comprises a slow wavetransmission line preferably in the form of a serpentined conductivetube, e.g. of copper. The microwave energy applied thereto by coupler 44is launched so that the energy effectively travels along the outside orskin of the conductor tube 40. Whereas most transmission lines aredesigned to minimize radiating fringing fields and consequentattenuation, in accordance with the present invention, frequency anddimensional parameters are selected to maximize fringing fields aroundthe illuminator 40. Moreover, as will be mentioned hereinafter, variousparameters are selected to concentrate the fringing field along the pathof the film 14 around the drum 30. The electromagnetic field,intersecting with the wet film, reacts therewith to generate heat in thecontained water thereby causing its migration to the film surface whereit is evaporated by the escaping air.

For the purpose of introducing background information, it is pointed outthat the electromagnetic field of course does not itself provide heatbut heat is generated as a consequence of the interaction between theelectromagnetic field and the moisture within the film 14. Moreparticularly, some materials, called lossless materials, do not respondto microwave emissions. However, other materials, known as lossymaterials, do respond to a microwave field. Normally, the base andgelatin emulsion of photographic film are considered lossless. However,the moisture present in wet film is lossy. As a consequence, in responseto an alternating electro-magnetic field, the water molecules on thefilm attempt to align themselves with the field. Each time the fieldreverses, the water molecules rotate to realign themselves. Thiscontinuous rotational action at microwave frequencies creates heat bymolecular friction, forcing the water to the surface and vaporizing it.The drying unit 12 in accordance with the present invention, constitutesan exceedingly useful and probably optimum configuration for presentingthe microwave energy to the film 14 in order to vaporize the moisturetherein. The air which is continually supplied to the unit 12 toreplenish the bearing, carries the vapor away, thus preventingcondensation.

It is pointed out that the direction of movement of the film 14 inFIGURE 2 is opposite to the direction of energy propagation along theiluminator 40. Thus, the wettest portion of the film is exposed to theweakest field intensity and the driest portion of the film in which themoisture is most tightly bound is exposed to the maximum fieldintensity.

Prior to proceeding to a detailed description of various structuralembodiments of the drying unit 12, further reference is made to FIGURE 2wherein a source 50 of coolant, e.g. water, is provided for dissipatingexcess heat generated as a consequence of the aforedescribed action. Thecoolant source is coupled by hose 52 to the microwave generator 42. Itis contemplated that coolant be pumped through the microwave generator42, and through the coupler 44 to the tubular illuminator 40. Thetubular illuminator 40 is hollow and thus passes the coolant to thedummy load 46 which can pass the coolant through a heat exchanger (notshown) prior to returning it to the coolant source 50 through hose 54.It is pointed out that the coolant path illustrated in FIGURE 2 is shownfor exemplary purposes only, and it will, of course, be appreciated thatother coolant paths could be utilized. For example, if justified,separate coolant paths can be provided to each of the various componentsto be cooled.

Attention is now called to FIGURE 3 which comprises a perspective viewof a preferred embodiment of drying unit 12 for drying material of afixed predetermined width. The drying unit 12 is comprised of a pair ofvertical frame pieces 60 and 62, which can be coupled to one another bytie rods 64. Mounted between the frame pieces 60 and 62 is a cylindricaldrum 66 fabricated of any lossless material, e.g. a solid plastic foammaterial 68. The surface of the drum 66 is provided with a plurality ofperforations 70 through which air can be exhausted. Mounted within andsubstantially coincident with the surface of the drum 66, is a pluralityof conductor or illuminator sections 72 extending parallel to the drumaxis. The opposite ends of each section 72 are coupled to difierentadjacent sections by U-shaped end pieces 73. Reduced end portions 74 onthe U-shaped pieces 73 are slidably received in the sections 72 fortuning purposes (FIGURE 4b).

Preferably, the sections 72 and perforations 70 extend only abouthalfway around the drum 66 as shown in FIGURE 3 inasmuch as it is onlynecessary that they be disposed adjacent the film path which, assuggested by FIGURES 1 and 2, will be adjacent the drum surface onlyabout halfway therearound. The frame pieces 60 and 62 define cutoutareas 78 in alignment with the center of the drum 66. The U-shaped end.pieces 73 can project beyond the plane of the pieces '60 and 62 (FIGURE3) and be retained within slots 82.

A perforated conductive ground plane 84 is concentrically disposedwithin the cylinder 66 and is held in place by a conductive band 86disposed within the cutout area 78. A sealing plate (not shown) isintended to fit over and seal the area 78 within the rim 87. Thus, thevolume enclosed by the drum 66 and sealing plate functions as a plenumchamber allowing the air introduced therein from port 88 to escapethrough the perforations 70 in the drum surface. The perforations 70 areproperly distributed over the drum surface so as to create a suitableair bearing for spacing the film .14 at a predetermined distance fromthe drum surface.

In order to create a satisfactory air bearing, it is additionallydesirable to provide wall portions 90' adjacent the sides of the drum66. As illustrated in FIGURES 3 and 4, the wall portions 90 can compriseintegral parts of the frame pieces 60 and 62. Each of the wall portions90 defines a series of air bleed channels 92 (FIGURES 3 and 5)immediately adjacent the drum surface. The air bleed channels 92function to permit air to escape out from under the film '14 as it rideson the air bearing over the drum surface. If due to the air pressure andthe weight of the film, the film is driven too far above the drumsurface, the amount of air bled through the channels 92 will increase,thus reducing the spacing between the film 14 and drum surface.

Attention is now called to FIGURE 6 which illustrates a schematiccross-sectional view of the drying unit 12 similar to the structuralview shown in FIGURE 5. FIG- URE 6, however, illustrates theinstantaneous polarity of each of the conductor sections in response tothe applied microwave energy. The length of each illuminator section 72from the midpoint of a U-shaped member at one end thereof to themidpoint of a U-shaped member at the opposite end thereof is selected tobe equal to approximately multiples of quarter wavelengths so thatcorresponding portions of adjacent sections will always define oppositepolarities. The polarities of the sections will, of course, reverse atthe frequency of the microwave energy utilized. As an example, amicrowave frequency of 2,450 megahertz, commonly called the S-band, canbe employed.

As a consequence of the polarity of adjacent conductor sections 100being opposite, an electromagnetic field rep resented by the field lines102 will be established extending from each illuminator section to anadjacent section. Thus, particularly considering sections 104 and 106 asan example, it will be noted that the field 102 extends above and belowthe drum surface as viewed in FIG- URE 6. In addition to the fieldestablished between adjacent sections, it is pointed out that a field isalso established between the conductor sections and the ground plane 84.

As the film 14 moves past the drum surface, spaced therefrom by the airbearing formed by the air escaping through perforations 70, the field102 will distort and tend to somewhat concentrate through the lossysubstance, i.e. the water carried by the film 14. It is desirable ofcourse that as large a portion of the field 102 as is possible beconcentrated within the filrn 14 extending parallel to the film path. Inorder to maximize the field strength through the film, the relationshipbetween variout parameters should be optimized. Thus, it is pointed outthat field concentration within the film 14 is dependent somewhat uponthe spacing between adjacent conductor sections, and the frequency ofthe electromagnetic energy employed. Additionally, it has been foundthat variations in the position of the ground plane 84 affect the degreeof concentration of the field within the film 14. Thus, it is desirableto critically and precisely position the ground plane 84.

It is pointed out that one of the favorable operating characteristics ofthe embodiment of FIGURES 3-5, is that by essentially conforming thefilm to the cylindrical surface of the drum, the films inherent tendencyto curl is minimized.

Attention is now called to FIGURE 7 which schematically illustrates analternative embodiment of the invention. More particularly, it will benoted that whereas all of the conductor sections of the serpentinedilluminator in the previously described embodiment were aligned alongthe periphery of a single curve, i.e. the drum surface, the illuminatorsections in the embodiment of FIGURE 7 are grouped along two spacedcurves. That is, the sections 110 in a lower row can be disposed andretained in the surface of a first drum (not shown) while the sections112 of an upper row can be disposed and retained in the surface of asecond drum (also not shown). In the embodiment of FIGURE 7, the film 14will be transported between the first and second rows of sections. It iscontemplated, but not necessary, that the sections 110 and 112 of FIGURE7 form part of a single continuous tube similar to the embodiment ofFIGURES 3-5, but however, serpentined around the film path. In theembodiment of FIGURE 7, it would of course be desirable to provide twoair hearings to thus space the film 14 from both the sections 110 andthe sections 112.

In a still further embodiment of the invention, as shown in FIGURE 8,the sections can be aligned in two parallel planes, rather than alongcurved rows, as shown in FIGURE 7. More particularly, a first group ofsections 114 can be arranged in a plane parallel to a second group ofsections 116 with the film 14 moving along a path between the groups ofsections 114 and 116. It is again contemplated that in the embodiment ofFIGURE 8, the illuminator be comprised of a single continuous tube withthe tube being serpentined around the film path 14. The sections 114 canbe disposed and retained in a first fiat surface (not shown) while thesections 116 can be retained and disposed in a second fiat surface (alsonot shown). As should be appreciated, in the utilization of theembodiment of FIGURE 8, it will be desirable to provide two air bearingsto space the film 14 from both the sections 114 and 116.

Although not specifically shown in the drawings, it should also beappreciated that the embodiment of the invention illustrated in FIGURES3-5 can be modified to employ a planar rather than cylindrical surface.In other words, the sections serpentined around the film path, shown inFIGURE 8, to define two planes of sections could be modified so that allof the sections would be aligned in a single plane with an air bearingbeing provided to space the film from that plane. It is also pointed outthat although it has been assumed that the several sections in eachembodiment form part of a single continuous conductor, it is notessential that this be so. Thus more than one conductor, each comprisedof several sections, could in fact be employed.

In order to enable an embodiment of the invention to accommodate variouswidths of films, means can be provided, as are schematically shown inFIGURE 9, for modifying the spacing between walls 120 and 122 definingthe air bearing side boundaries. In the schematically illustratedembodiment of FIGURE 9, the walls 120 and 122 are illustrated as beingoppositely threaded on a rotatable shaft 124 driven by positioner motor126. Thus as the shaft is rotated in one direction, the walls will moveaway from a center line and as the shaft is rotated in the otherdirection, the walls will move toward a center line. Other manual andautomatic arrangements will of course be apparent to those skilled inthe art. It is however pointed out that as the width of film being driedis changed, the power requirements of the illuminator also change. Thatis, inasmuch as there is an optimum amount of energy to be dissipated ina unit area of film, which optimum amount is dependent upon the rate offilm movement, the type of film material, and other factors, it isdesirable to vary the power delivered to the illuminator 128 as the areaof film being dried is varied in order to maintain an optimum balance.As a consequence, a control means 130 is provided which is responsive tothe positioner motor 126 for controlling the microwave power source 132delivering energy to the illuminator 128. Accordingly, as the positionermotor 126 moves the walls 120 and 122 together to accommodate a lesserwidth film, the control means 130 responds thereto by correspondinglyreducing the power delivered by source 132 to the illuminator 128.

Attention is now called to FIGURE which schematically illustrates afurther embodiment of the invention. It will be appreciated that in allof the embodiments thus far discussed, the conductor sections extendedsubstantially across the film width at right angles to the path of filmmovement. Such an arrangement may result in nonuniform film drying dueto node points of standing waves which may be established along theconductor sections. This is so because at the node points of course theelectromagnetic field intensity is substantially zero. Consequently, ifnode points on each of the conductor sections are in alignment, a narrowline along the film may not be exposed to an electromagnetic fieldintensity sufiicient to dry it at a rate commensurate with the otherportions of the film. "In order to assure that the node points along thevarious illuminator sections are somewhat misaligned, the conductorsections can be arranged at an angle with respect to the film path asshown in FIGURE 10.

Attention is now called to FIGURE 11 which illustrates a still furtherembodiment of the invention. Whereas all of the embodiments thus fardiscussed utilize either a single continuous tubular conductor or aplurality of conductors positioned in tandem, along the bearing surface,the embodiment of FIGURE 11 employs a series of quarter wavelengthsections with alternate sections being fed from different sources. Thus,a waveguide 142 for example can couple energy to each of illuminatorsections 144. Similiarly, a waveguide 146 can couple energy toilluminator sections 148, each section 148 being disposed between a pairof sections 144. The conductor sections 144 and 148 of FIGURE 11 can bealigned along a single surface, e.g. similar to the embodiment ofFIGURES 3-5 or can be arranged along two spaced surfaces with the film14 moving therebetween as represented in FIGURE 11. Additionally, theconductor sections 144 and 148 can be disposed at an appropriate anglewith respect to the film path 14 as is shown in the embodiment of FIG-URE 10.

Attention is now called to FIGURE 12 which schematically illustrates astill further embodiment of the invention in which the illuminatorsections 156 are formed by a series of successive bends which preferablyhave lengths equal to multiples of quarter wavelengths. By constructingthe illuminator sections as illustrated in FIGURE 12, a more uniformfield distribution through the film 14 is assured. Although alternatesections in FIG- URE 12 are illustrated as being fed from differentwaveguides or transmission lines, it should be appreciated that sectionsof the type shown in FIGURE 12 can be employed in lieu of straightsections in any of the aforedescribed embodiments of the invention.

From the foregoing, it should be appreciated that a drying apparatus hasbeen disclosed herein in which a piece of material, such as film orfibers, to be dried is transported through a microwave fringing fielddeveloped by an illuminator arrangement which can be fabricated in anyof various manners as is suggested by the several embodiments disclosedherein. Regardless of the particular illuminator arrangement, microwaveenergy propagated along the illuminator will establish a fringing fieldthrough which the material to be dried is passed. In accordance with asignificant feature of the invention, the material is transportedthrough the fringing field by supporting it on an air hearing or betweena pair of air bearings so as to eliminate the necessity for physicallycontacting the film. As a consequence, the film rides a predetermineddistance from the illuminator sections generating the fringing field.The moving air, in addition to supporting the film and spacing it fromthe illuminator sections, carries away the water vapor developed as aconsequence of the molecular heating in the film.

What is claimed is:

1. Apparatus for drying material comprising:

means for transporting said material along a predetermined path;

a transmission line disposed adjacent said path; and

means for propagating electromagnetic energy along said transmissionline to develop an electromagnetic fringing field intersecting saidpath.

2. The apparatus of claim 1 wherein said transmission line is comprisedof a plurality of sections each extending across said path.

3. The apparatus of claim 1 wherein said transmission line is comprisedof a plurality of sections extending substantially parallel to oneanother and to the plane of said path and substantially perpendicular tothe direction of said path.

' 4. The apparatus of claim 2 wherein said sections are disposed at anangle relative to the direction of said path.

5. The apparatus of claim 1 wherein said transmission line is comprisedof a plurality of sections arranged in first and second spaced rows,said first and second rows being disposed on opposite sides of saidpath.

6. Apparatus for drying material comprising:

means including a surface having openings therein for transporting saidmaterial along a predetermined path;

an illuminator disposed adjacent said path;

means for propagating electromagnetic energy along said illuminator todevelop an electromagnetic fringing field intersecting said path;

means for moving said material along said surfaces;

and

means for exhausting a gas through said openings to space said materialfrom said surface.

7. The apparatus of claim 6 wherein said illuminator extendssubstantially coincident with said surface.

8. The apparatus of claim 7 wherein said illuminator is serpentined insaid surface and includes a plurality of illuminator sections eachextending substantially perpendicular to the direction of said path.

9. The apparatus of claim 6 wherein said surface is substantiallycylindrical.

10. Apparatus adapted to dry material adapted to move along apredetermined path, said apparatus comprising:

a transmission line;

microwave genera-tor means coupled to said transmission line forpropagating energy therealong and for developing a fringing fieldintersecting said path; and

means creating a gas bearing between said material and said transmissionline for supporting said material in spaced relationship with respectthereto.

-11. The apparatus of claim 10 'wherein said transmission line includesat least one section extending substantially parallel to the plane ofand substantially perpendicular to the direction of said path.

12. Apparatus adapted to dry material adapted to move along apretetermined path, said apparatus comprising:

an illuminator comprising a hollow tube capable of passing a coolanttherethrough; microwave generator means coupled to said illuminator forpropagating energy therealong and for developing a fringing fieldintersecting said path; and

means creating a gas bearing between said material and said illuminatorfor supporting said material in spaced relationship with respectthereto.

'13. Apparatus adapted to dry material adapted to move along apredetermined path, said apparatus comprising:

an illluminator;

microwave generator means coupled to said illuminator for propagatingenergy therealong in a direction substantially opposite to the movementof said material along said path for developing a fringing fieldintersecting said path; and

means creating a gas bearing between said material and said illuminatorfor supporting said material in spaced relationship with respectthereto.

'14. Apparatus adapted to dry material adapted to move along apredetermined path, said apparatus comprising:

an illuminator; microwave generator means coupled to said illuminatorfor propagating energy therealong and for develop ing a fringing fieldintersecting said path; a surface defining openings therein; saidilluminator being disposed substantially coincident with said surface;and 7 means creating a gas bearing between said material and saidilluminator including means exhausting gas through said openings towardsaid path for supporting said material in spaced relationship withrespect to said illuminator.

15. The apparatus of claim 14 including a conductive perforated groundplane disposed adjacent said surface remote from said path.

16. The apparatus of claim 14 including first and second walls extendingparallel to said path on either side of said surface;

said walls defining gas bled channels therein adjacent said surface.

*1! The apparatus of claim 14 including first and second walls extendingparallel to said path on either side of said surface;

means for varying the spacing between said first and second walls. 18.The apparatus of claim 17 including means responsive to the spacingbetween said first and second walls for controlling said microwavegenerator means.

=19. The apparatus of claim 14 wherein said sunface is substantiallycylindrical defining a plenum chamber therein; and

means for supplying said gas to said plenum chamber. 20. Apparatusadapted to dry material adapted to move along a predetermined path, saidapparatus comprising:

an illuminator comprised of a first group of sections arranged along afirst surface and a second group of sections arranged along a secondsurface;

means for passing said material along said path between said first andsecond surfaces; microwave generator means coupled to said illuminatorfor propagating energy therealong and for developing a fringing fieldintersecting said path; andmeans creating a gas bearing between saidmaterial and said illuminator for supportin g said material in spacedrelationship with respect thereto.

References Cited UNITED STATES PATENTS 2,319,174 5/ 1943 Wilson 2l910.'61 X 2,588,218 3/1952 Dippel et al 3-4- 1 2,588,811 3/1952 Dippel et al34-1 3,263,052 7/1966 Jeppson et -al. 2'1910. 6'1 X 3,355,812 12/1967Bennett 341 JOHN J. CAMBY, Primary Examiner.

US. 01. X.R.

